140 Contributions to Indian Malacology. [No. 2, 



deflected inwards, but less sharply so than in O. Fairbanki, and it 

 does not conceal the umbilicus, the curve being more as in 0. Nilgiri- 

 cum. Aperture reversed, nearly circular, almost vertical, having 

 scarcely any inclination upwards. Peristome attached for a short 

 distance only, touching both the penultimate and ante-penultimate 

 whorls, double, both portions expanded, the outer more broadly re- 

 flexed, and interrupted for a short distance where attached, inner 

 peristome continuous. Length 0.12, breadth measured across the 

 peristome 0.12, shorter diameter 0.8, breadth of the aperture includ- 

 ing the peristome 0.6 inch. 



This is the largest form of the genus yet met with, exceeding even 

 the Labuan species O. Crespigni, H. Ad. It is much more pupa- 

 shaped than that kind is, but much less so than the two previously 

 described Indian forms, from both of which it may easily be distin- 

 guished by the apical whorls not being excentric, as well as by its 

 much greater size. 



As the figure of O. Fairbanki in the Proceedings of the Zoological 

 Society for 1866, PL XXXVIII, is rather too small to give a good 

 idea of the form, and the sculpture had been omitted, two figures are 

 given in the plate belonging to this paper, figs. 6, 6 a. For the 

 drawings I am indebted to the kindness of Captain Godwin Austen. 

 In fig. 6 a, representing the shell from below, the view is a little from 

 the side ; when seen from beneath in the line of the axis, the umbili- 

 cus is completely concealed by the last whorl, a character peculiar 

 to O. Fairbanki. 



From the figure just referred to in the Proceedings Zoological Society, 

 the idea is conveyed that Opisthostoma Fairbanki is a much smoother 

 species than O. Nilgiricam. This is due to the accident that the 

 draughtsman had only the former species before him, and copied the 

 figure of the other. In reality, the sculpture is about equally strong 

 on both forms, the only difference being, that it is a little closer in 

 O. Nilgiricum. 



In the 3rd supplement to Br. Pfeiffer's monograph of the Helicida 

 just published, I see with some surprise that he retains H. Adams' 

 genus Plectostoma. The author of that genus admitted in the Pro- 

 ceedings of the Zoological Society for 1865, p. 755, that it was identi- 

 cal with Opisthostoma, and subsequently in the Proceedings Zoological 



